Mirror holding mechanism in exposure apparatus, and device manufacturing method

ABSTRACT

Disclosed is a mirror holding system by which aberration resulting from deformation or positional deviation of an optical member, causing degradation of imaging performance, can be reduced whereby a desired optical performance is assured. Also disclosed is an exposure apparatus and a device manufacturing method based on such mirror holding system. The holding system includes a supporting member for supporting the optical element at a plurality of supports which are movable along an approximately radial direction about a predetermined point.

This application is a continuation application of co-pending U.S.application Ser. No. 10/778,810, filed Feb. 13, 2004, and entitled“Mirror Holding Mechanism In Exposure Apparatus, And DeviceManufacturing Method”. Aforementioned U.S. application Ser. No.10/778,810, filed Feb. 13, 2004, is incorporated by reference herein inits entirety.

This application claims the right of priority under 35 U.S.C. § 119 toJapanese Application Number 2003-035271 filed Feb. 13, 2003, in Japan.

FIELD OF THE INVENTION AND RELATED ART

This invention relates generally to a precision instrument on which anoptical member is mounted and, more particularly, to a projectionoptical system for use in an exposure apparatus, for example.Specifically, the invention concerns a holding system for an opticalmember, usable in an exposure apparatus for lithographic procedure formanufacture of semiconductor devices, image pickup devices such as CCD,or thin-film magnetic heads, for example, to obtain a more exact imagingrelationship in projection exposure in which an image of an originalsuch as mask or reticle (these terms being used alternately in thisspecification) is projected upon a workpiece to be processed.

Manufacture of devices based on photolithographic (printing) technologyuses a reduction projection exposure apparatus wherein a circuit patternformed on a mask is transferred onto a workpiece such as a wafer,through a projection optical system. The projection optical systemimages diffraction light from the circuit pattern upon the wafer, basedon interference.

In order to meet requirements to further reduction in size and thicknessof electronic instruments, devices to be mounted on the electronicinstruments must be largely integrated. Thus, further miniaturization ofa circuit pattern to be transferred, in other words, improvements ofresolution, has been required more and more. In order to obtain a higherresolving power, the wavelength of exposure light should be shortenedand, additionally, the numerical aperture (NA) of the projection lensshould be enlarged. Simultaneously, aberration of the projection opticalsystem has to be suppressed to a very low level.

If deformation occurs in an optical element such as lens or mirror,constituting the projection optical system, the light path inflectsbefore and after the deformation so that light rays that should beimaged upon a single point do not converge at that point, causingaberration. Such aberration produces a positional deviation that mayresult in short-circuit in a circuit pattern formed on a wafer. If, onthe other hand, the pattern size is widened to avoid short-circuit, itdirectly contradicts to the requirement of miniaturization.

Thus, in order to accomplish a projection optical system having smallaberration, it is very important to hold optical elements, constitutingthe projection optical system, within the projection optical systemwithout changing the shape thereof and the position thereof with respectto the optical axis, thereby to ensure that inherent optical performanceof the optical elements is best presented. Particularly, because ofenlargement of NA of recent projection optical systems, currentprojection lenses have a large diameter. The lens volume is thus largeand, as a result, deformation due to self weight easily occurs. Further,in exposure apparatuses that use extreme ultraviolet (EUV) light(hereinafter, “EUV exposure apparatus”), the projection optical systemhas to be constituted by a small number of reflecting elements (i.e.mirrors) because of its shortness of the wavelength (wavelength is about10 to 15 nm order). Thus, the precision required for the mirror shapeand positional precision with respect to the optical axis areextraordinarily strict.

An example of a method of holding an optical element without causingdeformation thereof, is a mask holding method (Registered JapanesePatent No. 3359330). In this method, a cone, a V-shaped groove and aplane are used and, by fixing the mask as like kinematic, the mask canbe held without deformation of the mask surface.

Since EUV exposure apparatuses are used for exposure of a circuitpattern, of a linewidth of 0.1 micron or less, the linewidth precisionis very strict. Regarding the mirror shape, only a deformation of about1 nm or less may be tolerable. It is therefore necessary to reproducethe mirror shape, determined when it was machined, at the time when thesame is incorporated into an EUV exposure apparatus.

However, the base material constituting the mirror is very soft, andonly a force (holding force) applied by a holding member for holding themirror will be sufficient to produce deformation of a few nanometers inthe mirror. Also, thermal expansion, vibration or deformation of theholding member may cause a positional deviation of the mirror.Furthermore, a mirror does not reflect all the exposure light, but itabsorbs 30% or more of the exposure light. The absorbed exposure lightproduces heat that causes thermal expansion of the mirror and it changesthe mirror shape and the mirror position with respect to the opticalaxis.

For theses reasons, it is very difficult to hold a mirror within aprojection optical system without a change in mirror shape or in mirrorposition with respect to the optical axis, to ensure desired opticalperformance.

It is accordingly an object of the present invention to provide aholding system by which aberration resulting from deformation orpositional deviation of an optical member, causing degradation ofimaging performance, can be reduced whereby a desired opticalperformance is assured.

It is another object of the present invention to provide an exposureapparatus and/or a device manufacturing method, based on such holdingsystem.

In accordance with an aspect of the present invention, there is provideda holding system, comprising: a supporting member for supporting anoptical element approximately at six points through three firstspherical members, wherein said supporting member has three grooves eachextending in an approximately radial direction about a predeterminedpoint, wherein the three grooves and the three first spherical membersare engaged with each other to position the optical element, and whereineach of the three grooves is movable in the approximately radiationdirection.

In one preferred form of this aspect of the present invention, the threegrooves are coupled to a fixing member through an elastic member and,through elastic deformation of the elastic member in the approximatelyradial direction, the three grooves can move.

The elastic member may be a resilient hinge.

The elastic member may be a leaf spring, wherein a direction normal tothe surface of the leaf spring may be substantially parallel to theapproximately radial direction.

Elastic deformation of the elastic member may occur substantially onlyin the approximately radial direction.

The holding system may further comprise an elastic supporting member forapplying an elastic force to the optical element in a direction pressingthe optical element against the first spherical member, wherein theelastic supporting member may be fixed to the fixing member.

The holding system may further comprise an elastic supporting member forapplying an elastic force to the optical element in a direction pressingthe optical element against the first spherical member.

The portion of the elastic supporting member that applies a force in adirection pressing the optical element against the first sphericalmember, may be made movable in the approximately radial direction.

The elastic supporting member may apply a force to the optical elementthrough a second spherical member.

The elastic supporting member and the second spherical member may engagewith each other substantially at a single point.

The holding system may further comprise an intermediate supportingmember being provided integrally with the optical element or beingarranged to support the optical element, wherein the intermediatesupporting member may have three first recessed portions, the threefirst recessed portions and the three first spherical members engagewith each other at three or more points, or they engage with each otherlinearly, and wherein, at contact points between the three firstrecessed portions and the three first spherical members, the firstrecessed portions may have a side-face shape of pyramid or cone.

The first recessed portions may have a shape of one cone, pyramid,truncated cone and truncated pyramid.

The holding system may further comprise a second intermediate supportingmember being provided integrally with the optical element or beingprovided on the optical element or being arranged to support the opticalelement, said second intermediate supporting member having three secondrecessed portions and three second spherical members corresponding tothe three second recessed portions, respectively, wherein each of thesecond recessed portions may engage with a second spherical member atthree or more points or they engage with each other substantiallylinearly, and wherein a force that the second spherical member appliesto the second recessed portion and a force that the first sphericalmember applies to the second recessed portion may be substantially inopposite directions.

The intermediate supporting member may be provided by a portion of theoptical element.

The intermediate supporting member may be a supporting frame, a relativeposition of which with reference to the optical element may besubstantially unchangeable.

The holding system may further comprise a coupling member for connectingthe optical element and the supporting member through the sphericalmember.

The coupling member may be a resilient hinge.

The three grooves may be disposed to define, therebetween, an angle notless than 90 deg. and not greater than 160 deg.

The three grooves may be disposed to define, therebetween, an angle notless than 110 deg. and not greater than 130 deg.

The three grooves may have a V-shape in cross-section, contacting thethree first spherical members approximately at two points.

The optical element may be a reflection member.

In accordance with another aspect of the present invention, there isprovided an exposure apparatus, comprising: an illumination opticalsystem for illuminating a pattern, formed on a mask or a reticle, withlight from a light source; a projection optical system for projectinglight from the pattern to a workpiece to be exposed; and a holdingsystem as recited in claim 1, wherein at least one of said illuminationoptical system and said projection optical system includes said holdingsystem.

In one preferred form of this aspect of the present invention, lightused in said apparatus may be extreme ultraviolet light.

In said exposure apparatus, an ambience of a light path along whichexposure light passes may be filled with a high vacuum or substantiallyfilled with a helium gas.

In accordance with a further aspect of the present invention, there isprovided a device manufacturing method, comprising the steps of:exposing a workpiece to be exposed, by use of an exposure apparatus asrecited in above; and performing a predetermined process to the exposedworkpiece.

In accordance with a yet further aspect of the present invention, thereis provided a holding system, comprising: a supporting member forsupporting an optical element by means of a plurality of supports;wherein said plurality of supports are movable in an approximatelyradial direction about a predetermined point.

In accordance with a still further aspect of the present invention,there is provided an exposure apparatus, comprising: an illuminationoptical system for illuminating a pattern, formed on a mask or areticle, with light from a light source; a projection optical system forprojecting light from the pattern to a workpiece to be exposed; and aholding system as recited above, wherein at least one of saidillumination optical system and said projection optical system includessaid holding system.

These and other objects, features and advantages of the presentinvention will become more apparent upon a consideration of thefollowing description of the preferred embodiments of the presentinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic and perspective view for explaining a mirrorholding method according to an embodiment of the present invention.

FIG. 2 is a sectional view taken along a plane A-A in FIG. 1.

FIG. 3 is a sectional view taken along a plane L-L and as seen from theabove.

FIG. 4 is a sectional view for explaining a coupling rod with an elastichinge.

FIG. 5 is a schematic view for explaining an example of improvingvibration resistive rigidity.

FIG. 6 is a schematic view for explaining an example wherein grooves andelastic hinges are formed in separate structures.

FIG. 7 is a schematic view of a general structure of an exposureapparatus according to an embodiment of the present invention.

FIG. 8 is a flow chart for explaining manufacturing procedure formicrodevices such as semiconductor chips (IC or LSI), LCD, or CCD, forexample.

FIG. 9 is a flow chart for explaining details of a wafer process at step4 in FIG. 8.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of mirror holding method and exposure apparatusaccording to the present invention will now be described with referenceto the attached drawings. However, the invention is not limited to theseembodiments, and components may be replaced alternately within the scopeof the invention. For example, in the embodiments to be described below,the invention is applied to a projection optical system 530 of anexposure apparatus 500, the invention may be applied to an illuminationoptical system 514 of the exposure apparatus 500 or to any other opticalsystem well-known in the art. In the drawings, the same referencenumerals are assigned to corresponding elements, and duplicatedescription therefor will be omitted. FIG. 1 is a schematic and sideview of a mirror holding method 100 according to an aspect of thepresent invention.

Denoted at 110 is a mirror for imaging light on the basis of reflection.The mirror 110 has a reflection surface on which a multilayered film forreflecting light is provided, such that light is strengthened by themultilayered film. A multilayered film that can be applied to the mirror110 may be Mo/Si multilayered film wherein molybdenum (Mo) layers andsilicon (Si) layers are accumulated alternately or Mo/Be multilayeredfilm wherein Mo layers and beryllium (Be) layers are accumulatedalternately. However, the multilayered film is not limited to thesematerials, and any other multilayered films having similar functions andeffects may be used.

Denoted at 112 are recessed portions which are distributed at 120-degreepitch along the same circumference. However, the recessed portions maynot be provided at 120-degree pitch, but they may be disposed in anangular range from not less than 90 deg. to not greater than 160 deg,more preferably, 110 deg. to 130 deg. This will be described in greaterdetail, with reference to FIG. 2.

FIG. 2 is a sectional view taken along a plane A-A in FIG. 1. Therecessed portions 112 are formed to be opposed to both sides of a flangesurface of the mirror, and they have a conical shape. The recessedportion may be formed directly on the mirror, or it may be provided on amember that is formed integrally with the mirror. Alternatively, it maybe formed on a member that supports the mirror in the counter-gravitydirection.

Denoted at 114 are spherical members. Each spherical member 114 has ashape of perfect sphericity, and it engages with the slant surface ofthe recessed portion 112 by linear contact, by which it is held. Here,by combination of a spherical member and a recessed portion of conicalshape, substantial linear contact is assured. However, the recessedportion may be formed with a shape of triangular pyramid to assurethree-point contact. Other forms will be described below.

Denoted at 116 is a support table. The support table 116 has sphericalmembers 118 (to be described below) which are in contact with the mirror110, and grooves 120 for receiving the spherical members 118. Itsupports the mirror 110. The supporting table 116 is a ring-like platemember disposed about the optical axis, and it is desirable that thetable 116 is made of a material having substantially the same orcorresponding linear expansion coefficient as that of the mirror 110.

The spherical members 118 are disposed at 120-deg. pitch to meet therecessed portions 112 formed at the lower portion of the flange(intermediate support member) of the mirror 110. Since the sphericalmembers 118 are distributed substantially equidistantly along acircumferential direction of the mirror 110, the mirror 110 can bestable on the support member 116. As a matter of course, since this isjust to keep a desired mirror shape, any other pitch, other than 120deg. pitch, may be used provided that the desired mirror shape can bemaintained. Here, the spherical member 118 is a member at least of whichhas a shape of perfect sphericity, and the outer circumference of itengages with the recessed portion 112 formed at the lower portion of theflange of the mirror 110. In this example, the recessed portion 112 hasa conic shape, but it may have a shape of pyramid with angular cornersof a number n (n is an integer not less than 3), such as triangularpyramid or square pyramid, for example. Alternatively, it may be arecessed portion having a similar side face or faces like that of a coneor pyramid, for example, truncated cone or truncated pyramid. Where arecessed portion of pyramid shape is used, the portion to be engagedwith a spherical member should have a shape similar to the side face ofthe pyramid and, additionally, the spherical member and the recessedportion should engage at three points or more.

Here, the cone or pyramid described above may be provided in a portionoutside the effective region of the mirror (optical element).Alternatively, it may be provided a support member (supporting frame)that is formed integrally with the mirror or that has a substantiallyfixed relative position with respect to the mirror. As a furtheralternative, it may be provided on a supporting member (supportingframe) that supports the mirror at plural point (three points, forexample). Here, the member on which such cone or pyramid is formed willbe referred to as an “intermediate support member”.

The spherical member 118 is mounted on a groove 120 which is movable ina radial direction of the support table 116. Namely, the groove 120 hasa freedom in the radial direction. Here, in order to assure engagementof the spherical member 118 with the recessed portion 112, the recessedportion may be “co-rubbed” with use of the spherical member 118. Here,“co-rubbing” is to assure substantial linear contact between thespherical member and the recessed portion (conic shape).

The grooves 120 are formed on the support table 116 at 120-deg. pitch,in radial directions. The disposition of the grooves 120 corresponds tothe recessed portions 112. The groove 120 functions to allow motion ofthe spherical member 118 in the radial direction but to restrict motionthereof in the circumferential direction. It has a sectional shape ofV-shape, so that the spherical member 118 engages with flat faces of thegroove at two points. Namely, by means of three grooves 118, the mirror110 is supported at six points with the spherical members 118 (i.e.kinematic support). Thus, without excessive confinement to the mirror110, the posture of the mirror can be maintained.

Now, the structure of the supporting table 116 will be described indetail, with reference to FIG. 3.

FIG. 3 is a sectional view taken along a plane L-L in FIG. 2 and as seenfrom the above. As has been already described above, the support table116 has grooves 120 provided at 120-deg. pitch about a predeterminedpoint and in approximately radial directions. Here, the grooves 120 maynot be provided at 120-deg. pitch as like the recessed portions. Thegrooves may be formed with a mutual angle relation of not less than 90deg. and not greater than 160 deg., more preferably, not less than 110deg. and not greater than 130 deg.

Around the groove, there are notches formed perpendicularly to and inparallel to the groove 120 so as to sandwich, therebetween, the twocontact points for supporting the spherical member 118, and an elastichinge K is provided there. With this structure, even if there occursthermal expansion of the mirror 110 in response to changes intemperature environment, the elastic hinge K links in parallel so thatexpansion in the radial direction is allowed. This effectively preventspositional deviation of the mirror center with respect to the opticalaxis.

As regards the spherical member 118 and the groove 120, in order toavoid a change in posture of the mirror 110 resulting from deformationat the two contact points and also to assure idealistic six-pointcontact, they should have high stiffness and the friction should bereduced as much as possible (low friction coefficient). As regards thematerials for the spherical members 118 and grooves 120 that satisfyhigh stiffness and low friction coefficient, ceramics, metal having asurface subjected to hardening heat treatment, or film coating based onion plating such as DLC, for example, may be used.

Referring back to FIG. 2, denoted at 112 is a connecting rod thatfunctions to secure the spherical members 114 and 118 to the mirror 110and to connect the spherical member 118 to the support table 116. Inthis example, the spherical member 118 has an integral structure withthe connecting rod 122.

Denoted at 124 is a pressing spring, and denoted at 126 is a nut for thepressing spring. By using these two parts, the spherical member 118 ispressed against the support table 116, whereby a large rigidity isassured. However, the structure is not limited to this. In place ofusing a spring, a structure for attracting the connecting rod 122 may beused, with similar advantageous effects. Further, in place of theconnecting rod 122, a string or wire may be used to provide similarfunctions.

In the structure shown in FIG. 2, described above, if the structure isproduced idealistically, the mirror can be stably held on the supporttable 116. If however there is a manufacturing error or assemblingerror, the connecting rod 122 may tilt and thus a moment load may beapplied to the mirror 110 through the spherical member 118. In order toavoid it, the following method may be used.

FIG. 4 shows an example wherein the connecting rod 122 is provided withan elastic hinge. In the drawing, the central portion of the connectingrod is thinned to provide a flexible hinge M there. With thisarrangement, even if a moment load is applied to the mirror 110, suchload can be absorbed by the hinge M. Thus, idealistic support isassured.

Only by the self weight thereof, the mirror 110 can be stable upon thesupport member 116 through cooperation of the spherical members 118 andgrooves 120. However, while taking into account the possibility ofvibration to be applied during transportation of the optical systemhaving the holding system 100 incorporated therein, in this example, apressing spring 128 and a nut 130 for the pressing spring are used topress the spherical member 114 against the mirror 110, thereby toincrease the rigidity.

The rigidity improvement is not limited to this structure. FIG. 5 showsan example of increasing the vibration rigidity. Denoted at 132 is anelastic support member having two flexible hinges. In the top plan viewin FIG. 5, the flexible hinge is denoted at J, and functions like theflexible hinge K described hereinbefore. Since the flexible hinge J isprovided to define a parallel linkage, even if thermal expansion of themirror occurs in response to a change in temperature environment,expansion thereof in the radial direction is allowed. This effectivelyprevents a positional deviation of the mirror center with respect to theoptical axis.

In the side view in FIG. 5, there is a flexible hinge N that allowsshift in the optical axis direction in response to a change intemperature environment. Also, it enables absorption of vibrationapplied from the outside. At the engagement between the elastic supportmember 132 and the spherical member 114, they engage with each other bypoint contact. For idealistic contact, they have a large stiffness andthe friction should be reduced as much as possible. As regards thematerials that satisfy high stiffness and low friction coefficient,ceramics, metal having a surface subjected to hardening heat treatment,or film coating based on ion plating such as DLC, for example, may beused.

The elastic support member 132 may function to continuously or normallyclamp the mirror 110. Depending on the required mirror surface precisionor vibration resisting characteristics, whether it should be usedcontinuously or used only for transportation may be determinedappropriately.

With the structure described above, the mirror 110 can be supported onthe support table 116 without surface deformation regardless of thermalexpansion thereof. Here, it should be noted that, although in theforegoing embodiments the grooves and elastic hinges are provided on thesupport table 116, these portions may be formed as a separate structure,and substantially the same advantageous effects are obtainable thereby.FIG. 6 shows it, and illustrates an example wherein the grooves andelastic hinges are provided in a separate structure. Denoted at 134 aregroove members that embody the structure described above. By providingthem in a similar structure like the support table 116, substantiallythe same advantageous effects are obtainable. The material and surfacetreatment described hereinbefore similarly apply to the groove members134, and duplicate description will be omitted here.

The foregoing embodiments have been described with reference to a mirroras an optical element. However, it may be any other optical element suchas lens, parallel planar plate, diffractive optical element, orpolarizing plate, for example.

In the foregoing embodiments, the grooves provided on the support table116 are made movable in the radial directions. However, as a matter ofcourse, the recessed portions may be made movable in the radialdirections, with similar advantageous effects. As a further alternative,the recessed portions may be formed on the support table, while thegrooves may be formed on the mirror (optical element).

In the embodiments described above, desirably, the grooves and supporttable are made relatively movable in a direction perpendicular to theoptical axis of the mirror (optical element). Preferably, the movementdirection may be the same as an approximately radial direction about theoptical axis of the mirror (optical element). As a specific structure,preferably, the groove (or recessed portion) and the support table (ormirror) may be connected through a member (such as a leaf spring, forexample) that can be easily deformed with respect to a predetermineddirection perpendicular to the optical axis of the mirror (opticalelement) (preferably, in an approximately radial direction about themirror optical axis) but can not be easily deformed with respect to adirection parallel to the mirror optical axis. As a matter of course,the structure may be that the recess (or groove) and the mirror (opticalelement) may be connected to each other through such a member. Here, asregards the aforementioned movement direction, it may be in anapproximately radial direction about a predetermined point inside aneffective region of light impinging on the mirror, but not in theapproximately radial direction about the optical axis of the mirror(optical element). More preferably, it may be in an approximately radialdirection about a predetermined point adjacent the gravity centerposition of the effective region of the light incident on the mirror.

Referring now to FIG. 7, an embodiment of exposure apparatus 500according to the present invention will be described. FIG. 7 is aschematic view of a general structure of the exposure apparatus 500.

The exposure apparatus 500 is a projection exposure apparatus whereinEUV light (e.g. wavelength 13.4 nm) is used as illumination light forexposure, and a circuit pattern formed on a mask 520 is projected andlithographically transferred to a workpiece 540 to be exposed, inaccordance with a step-and scan method or step-and-repeat method, forexample. This type of exposure apparatus is particularly suitably usableto lithographic process for submicron or quarter-micron order. In thisembodiment, description will be made to an example of step-and-scan typeexposure apparatus, called a scanner. Here, the step-and-scan method isan exposure method in which a wafer is continuously scanned (scanninglymoved) relative to a mask so that a mask pattern is lithographicallytransferred to the wafer while, on the other hand, after completion ofthe exposure of one shot, the wafer is moved stepwise for exposure of asubsequent exposure region. On the other hand, the step-and-repeatmethod is an exposure method in which, each time a zone exposure iscompleted, the wafer is moved stepwise toward a subsequent exposureregion.

Referring to FIG. 7, the exposure apparatus 500 comprises anillumination system 510, a mask 520, a mask stage 525 for carrying themask 520 thereon, a projection optical system 530, a workpiece 540 to beexposed, a wafer stage 545 for carrying the workpiece 540 thereon, analignment detecting mechanism 550, and a focus position detectingmechanism 560.

As shown in FIG. 7, since EUV light has low transmissivity toatmosphere, at least the light path along which the EUV light passes(that is, the whole optical system) may preferably be filled with avacuum ambience VC.

The illumination system 510 is arranged to illuminate a mask 520 withEUV light (e.g. wavelength 13.4 nm) of arcuate shape defined withrespect to an arcuate view field of the projection optical system 530.It includes an EUV light source 512 and an illumination optical system514.

The EUV light source 512 comprises a laser plasma light source, forexample. In the laser plasma light source, pulsed laser light of largeintensity is projected on a target material placed inside a vacuumcontainer, whereby a high-temperature plasma is produced. EUV light of awavelength of 13 nm order, for example, emitted from the plasma is used.As regards the target material, metal film, gas jet or liquid drops maybe used. In order to improve the average intensity of emitted EUV light,the repetition frequency of the pulse laser should be high, andgenerally, the laser is operated at a repetition frequency of a few KHz.

The illumination optical system 514 comprises a condensing mirror 514 aand an optical integrator 514 b. The condensing mirror 514 a serves tocollect EUV light being approximately isotropically emitted from thelaser plasma. The optical integrator 514 b has a function forilluminating the mask 520 uniformly with a predetermined numericalaperture. Also, the illumination optical system 514 includes an aperture514 c disposed at a position optically conjugate with the mask 520, forrestricting the illumination region on the mask into an arcuate shape.The holding system 100 of the present invention can be applied to thecondensing mirror 514 a and the optical integrator 514 b which areoptical members constituting the illumination optical system 514.

The mask 520 is a reflection type mask, and it has a circuit pattern (orimage) formed thereon which pattern is going to be transferred. The maskis supported on and moved by a mask stage 525. Diffraction lightproduced from the mask 520 as illuminated is reflected by the projectionoptical system 530, and is projected on the workpiece 540 to be exposed.The mask 520 and the workpiece 540 are disposed in an opticallyconjugate relationship with each other. The exposure apparatus 500 inthis embodiment is a step-and-scan type exposure apparatus, and byscanning the mask 520 and the workpiece 540, the pattern of the mask 520is projected and transferred onto the workpiece 540 in a reduced scale.

The mask stage 525 supports the mask 520, and it is connected to amoving mechanism (not shown). Any structure well-known in the art may beapplied to the mask stage 525. The moving mechanism not shown in thedrawing comprises a linear motor, for example, and it drives the maskstage 525 at least in X direction, thereby to move the mask 520. Theexposure apparatus 500 operates to scan the mask 520 and the workpiece540 in synchronism with each other.

Here, the scan direction along the plane of the mask 520 surface orworkpiece 540 surface will be referred to as X, a directionperpendicular to that direction will be referred to as Y, and adirection perpendicular to the mask 520 surface or workpiece 540 surfacewill be referred to as Z.

The projection optical system 530 includes a plurality of reflectionmirrors (multilayered-film mirrors) 530 a to project a pattern formed onthe mask 520 surface onto the workpiece 540 (image plane) in a reducedscale. The number of mirrors 530 a may be about four to six. In order toobtain a wide exposure region with a smaller number of mirrors, only anarrow arcuate region (ring field) spaced from the optical axis by acertain distance, may be used, while the mask 520 and the workpiece 540are scanned simultaneously. This enables transfer of a wide area.

The numerical aperture (NA) of the projection optical system is about0.1 to 0.3. The holding system 100 of the present invention can beapplied to the mirrors 530 a, for example, which are optical membersthat constitute the projection optical system 530. The holding system100 is connected to a barrel of the projection optical system 530through a member, not shown. Thus, the in the projection optical system530, aberrations due to deformation and positional deviation of anoptical member, which would cause degradation of the imagingperformance, can be reduced effectively and a desired opticalperformance can be accomplished.

The workpiece 540 is a wafer, in this embodiment. However, it may be aliquid crystal base substrate or any other members to be processed. Theworkpiece 540 has a photoresist applied thereto.

The photoresist application step includes a pre-process, an adhesionenhancing agent applying process, a photoresist applying process, and apre-baking process. The pre-process includes washing and drying. Theadhesion enhancing agent applying process is a surface improving process(hydrophobic process based on application of a surface active agent) forimproving the adhesion between the photoresist and the substrate. Anorganic film such as HMDS (hexamethyl-disilazane) may be applied bycoating or vapor deposition. The pre-baking is a baking (sintering)process, but it is mild as compared with that to be carried out afterthe development. This process is to remove the solvent.

The wafer stage 545 has a wafer chuck 545 a to support the workpiece540. The wafer stage 545 moves the workpiece in X, Y and Z directions byuse of a linear motor, for example. The mask 520 and the workpiece 540are scanned (moved) in synchronism with each other. Also, the positionof the mask stage 535 and the position of the wafer stage 545 aremonitored by means of a laser interferometer, for example, and they aredriven at a constant speed ratio.

The alignment detecting mechanism 550 has a function for measuring thepositional relation between the mask 520 position and the optical axisof the projection optical system 530, as well as the positional relationbetween the workpiece 540 position and the optical axis of theprojection optical system 530. Also, it functions to set the positionsand angles of the mask stage 525 and the wafer stage 545 so that aprojected image of the mask 520 is registered with a predeterminedposition of the workpiece 540.

The focus position detecting mechanism 560 measures the focus positionupon the workpiece 540 surface, and it controls the position and angleof the wafer stage 545 thereby to continuously hold the workpiece 540surface at the imaging position of the projection optical system 530.

In exposure operation, the EUV light produced by the illumination device510 illuminates the mask 520, and the pattern provided on the mask 520surface is imaged upon the workpiece 540 surface. In this embodiment,the image plane has an arcuate shape (ring-like shape) and, by scanningthe mask 520 and the workpiece 540 at a speed ratio corresponding to thereduction magnification ratio, the whole surface of the mask 520 isexposed.

Next, referring to FIGS. 8 and 9, an embodiment of a devicemanufacturing method which uses an exposure apparatus 500 describedabove, will be explained.

FIG. 8 is a flow chart for explaining the procedure of manufacturingvarious microdevices such as semiconductor chips (e.g., ICs or LSIs),liquid crystal panels, or CCDs, for example. In this embodiment,description will be made to an example of semiconductor chip production.Step 1 is a design process for designing a circuit of a semiconductordevice. Step 2 is a process for making a mask on the basis of thecircuit pattern design. Step 3 is a process for preparing a wafer byusing a material such as silicon. Step 4 is a wafer process which iscalled a pre-process wherein, by using the thus prepared mask and wafer,a circuit is formed on the wafer in practice, in accordance withlithography. Step 5 subsequent to this is an assembling step which iscalled a post-process wherein the wafer having been processed at step 4is formed into semiconductor chips. This step includes an assembling(dicing and bonding) process and a packaging (chip sealing) process.Step 6 is an inspection step wherein an operation check, a durabilitycheck an so on, for the semiconductor devices produced by step 5, arecarried out. With these processes, semiconductor devices are produced,and they are shipped (step 7).

FIG. 9 is a flow chart for explaining details of the wafer process. Step11 is an oxidation process for oxidizing the surface of a wafer. Step 12is a CVD process for forming an insulating film on the wafer surface.’Step 13 is an electrode forming process for forming electrodes upon thewafer by vapor deposition. Step 14 is an ion implanting process forimplanting ions to the wafer. Step 15 is a resist process for applying aresist (photosensitive material) to the wafer. Step 16 is an exposureprocess for printing, by exposure, the circuit pattern of the mask onthe wafer through the exposure apparatus described above. Step 17 is adeveloping process for developing the exposed wafer. Step 18 is anetching process for removing portions other than the developed resistimage. Step 19 is a resist separation process for separating the resistmaterial remaining on the wafer after being subjected to the etchingprocess. By repeating these processes, circuit patterns are superposedlyformed on the wafer.

With these processes, high-quality microdevices can be manufactured.

As described, a device manufacturing method that uses an exposureapparatus as well as a device as a product thereof are also in the scopeof the present invention.

While preferred embodiments of the present invention have been describedin the foregoing, the invention is not limited to them. Many changes andvarious modifications are possible within the scope of the invention. Asan example, the holding system of the present invention may be used tosupport a mask or a wafer.

While the invention has been described with reference to the structuresdisclosed herein, it is not confined to the details set forth and thisapplication is intended to cover such modifications or changes as maycome within the purposes of the improvements or the scope of thefollowing claims.

1. A holding system, comprising: a supporting member for supporting anoptical element approximately at six points through three firstspherical members, wherein said supporting member has three grooves eachextending in an approximately radial direction about a predeterminedpoint, wherein the three grooves and the three first spherical membersare engaged with each other to position the optical element, and whereineach of the three grooves is movable in the approximately radiationdirection.